Improve Windows Terminal UI tests

- Refactored generic terminal testcase out of the Windows I/O testcase
- Getstdinout is now triggered by a sentinel being overwritten by the
  copy operation
- Wait for the window to be ready before sending keys
- Add ui_tests.bat to run ui_tests correctly on Windows

Change-Id: Id132afbd51999a7db3974c0fddd5016c35c7a335
Merge "Improve Windows Terminal UI tests"